1. Field of the Invention
The present invention relates to automatic adaptive beam positioning antennas for mobile satellite communications. More particularly, the invention relates to fixed arrays of several omnidirectional antennas, weighted and combined to form at least one receive beam adaptively pointed in the direction of a corresponding incoming signal.
2. Description of the Related Art
Satellite communications is generally performed at microwave frequencies. Power levels at such frequencies normally require a directional gain antenna coupled to a receiver and pointed at the satellite with which the receiver is communicating.
With a fixed ground station receiver, the need for directional gain is of no consequence, because (assuming a geostationary satellite) the antenna can be positioned appropriately during site installation and never repositioned. This is also true with some mobile installations in which the vehicle having the receiver is stationary while communicating with the satellite.
In "true" mobile satellite communications, however, where the vehicle is moving while communicating with the satellite and/or while the satellite is also moving, the need for directional gain can pose a problem. If a mechanically positioned directional antenna (e.g., a tracking dish) is used, it must be continually positioned and repositioned. Mechanically actuated tracking can be slow, however, being dependent on the power of the servo motor and/or the weight of the antenna. Alternatively, an omnidirectional antenna can be used to receive signals in a true mobile satellite communications application. These antennas, however, generally lack the requisite gain to adequately perform in this application.
Accordingly, a need exists for a digital signal processing technique to achieve an automatically, adaptive electronic beam positioning system for mobile satellite communications requiring an antenna that can be rapidly and continually steered in the direction of incoming signals.